Ms Nauert said North Korea’s vice chairman Kim Yong Chol had agreed to meet on or about 12 July in Panmunjom with an American delegation, but the meeting did not materialise.

It comes after Mr Trump released a “very nice note” from Mr Kim, signalling his optimism about efforts to end the nuclear stand-off with North Korea.

He shared the four-paragraph letter on Twitter, in which Mr Kim describes their 12 June summit – and the resulting joint statement – as the “start of a meaningful journey”.

“I firmly believe that the strong will, sincere efforts and unique approach of myself and Your Excellency Mr. President aimed at opening up a new future between the DPRK and the U.S. will sure surely come to fruition,” Mr Kim writes.

“I deeply appreciate the energetic and extraordinary efforts made by Your Excellency Mr. President for the improvement of relations between the two countries and the faithful implementation of the joint statement,” he adds.

Mr Pompeo travelled to Pyongyang for two days last week with the aim of fleshing out denuclearisation commitments, insisting the talks were making progress.

But Pyongyang warned that the future of the peace process was being jeopardised by “unilateral and gangster-like” US demands.